1. Field of the Invention
This invention relates to an electrophotographic conductive member, such as a charging member, a developer carrying member, an intermediate transfer member or a transfer material transporting member, and an electrophotographic apparatus having the electrophotographic conductive member.
2. Related Background Art
Various systems, such as an electrophotographic system, a thermal transfer system and an ink-jet system, have conventionally been employed in an image forming apparatus. Of these, an image forming apparatus employing the electrophotographic system, what is called an electrophotographic apparatus, is superior to an image forming apparatus employing other systems due to its high speed, high image quality and lack of noise.
The electrophotographic system is a system in which the surface of an electrophotographic photosensitive member is primarily electrostatically charged (a primary charging step), thereafter an electrostatic latent image is formed on the surface of the electrophotographic photosensitive member by an exposure (an exposure step), this electrostatic latent image is developed with a toner to form a developed image (a developing step), and thereafter this developed image is transferred to a transfer material (a transfer step). In the primary charging step or the transfer step, a charging member, such as a primary charging roller or a transfer charging roller, is used. In the developing step, a developer carrying member, such as a developing roller, is used.
In addition, not only monochrome electrophotographic apparatuses, but also polychrome (color) electrophotographic apparatuses (color electrophotographic apparatus) have become popular.
Various systems are employed in such color electrophotographic apparatuses. For example, well known are an intermediate transfer system in which primary charging, exposure and development are successively performed for each color by means of a single electrophotographic photosensitive member, and respective-color toner images are primarily sequentially transferred onto an intermediate transfer member (such as an intermediate transfer drum or an intermediate transfer belt), where the toner images thus transferred are thereafter secondarily transferred in a lump onto a transfer material to form a color image; and an in-line system in which respective-color toner images are respectively formed in respective-color image forming sections disposed in series (each having an electrophotographic photosensitive member, a primary charging means, an exposure means, a developing means, a transfer means and so forth), and the toner images thus formed are sequentially transferred to a transfer material and transported to the respective image forming sections, in turn, to form a color image.
The color electrophotographic apparatus of an intermediate transfer system has an advantage in that a great variety of transfer materials can be selected without regard to the differences in their width, length and thickness because it is unnecessary to process or control the transfer material (such as paper), e.g., hold it on a gripper, attract it to the electrophotographic photosensitive member or make it have a curvature. The color electrophotographic apparatus of an in-line system also has an advantage in that a color image is formed through one step and images can be reproduced at a high speed.
However, these electrophotographic conductive members, such as a charging member, a developer carrying member, an intermediate transfer member and a transfer material transporting member, have the following technical problems.
The electrophotographic conductive members, such as a charging member, a developer carrying member, an intermediate transfer member and a transfer material transporting member, are commonly produced using thermoplastic resin compositions. Also, in providing the electrophotographic conductive members with conductivity, a method is commonly used in which a conductive filler is dispersed in the thermoplastic resin composition and may agglomerate when its surface energy is higher than the surface energy of the thermoplastic resin in the thermoplastic resin composition.
If the conductive filler agglomerates, it may disperse poorly, resulting in a non-uniform density of the conductive filler in the thermoplastic resin composition. This makes the electrical resistance of the electrophotographic conductive members unstable and makes any desired electrical resistance unachievable. Also, if the non-uniformity density of the conductive filler in the thermoplastic resin composition results in protrusions or the like on the surfaces of the electrophotographic conductive members, faulty reproduced images may appear or leaks may occur due to these protrusions. In such a case, it is difficult to obtain satisfactory products and their yield may be poor, resulting in a high production cost.
As a countermeasure for these problems, Japanese Patent Application Laid-open No. H03-089357 discloses a technique in which a conductive filler and every kind of dispersing agent (such as wax) are mixed.
However, the technique disclosed in Japanese Patent Application Laid-open No. H03-089357 requires the use of a dispersing agent in an amount equal to or greater than the amount of the conductive filler. For example, where the electrophotographic conductive members having the desired conductivity are formed, the total amounts of the conductive filler and dispersing agent may inevitably be close to about 50% of the amount of the thermoplastic resin composition. This has, in some cases, caused a substantial decrease in physical properties of the thermoplastic resin composition or the electrophotographic conductive members making use of the same.
A cationic surface-active agent is also available as a dispersing agent that may be added in a small quantity. The cationic surface-active agent, however, tends to bleed. Hence, the electrical resistance on the surfaces of the electrophotographic conductive members may change, or some bleeding matter may contaminate the electrophotographic photosensitive member or cause a break in the electrophotographic photosensitive member at its surface. This resulted in faulty reproduced images in some cases.